1. Field of the Invention
The present invention relates to a novel process for producing brominated acenaphthylene condensates (Con-BACN) starting from acenaphthene, more particularly for producing brominated acenaphthylene condensates having a general formula, ##STR3## (x represents an integer from 1 to 2, y from 1 to 6 and n 2 or more), more specifically having an elementary unit as defined below: ##STR4## (n and n' are integers between 1 and 6). Further, the present invention relates to a process for separating and recovering brominated acenaphthylene condensates in powder form.
In recent years, it has been a general trend to apply a fire-retarding treatment to inflammable resins such as polyethylene, polypropylene and ethylene-propylene rubber from the standpoint of fire-prevention, and addition of various fire-retarding agents to resins is known for that purpose. Further, wires and cables as well as various instruments used in atomic reactors, breeder reactors and ionization radiation generators are necessarily fire-retarding from the standpoint of safety. Therefore, insulation coating materials and various resin compositions used for these wires must be not only fire-retarding but also radiation-resistant.
Brominated acenaphthylene condensates which are known as excellent compounds having good fire-retarding and radiation-resistant properties could be grafted to a resin by applying free radical generation treatment due to the double bonding in their molecules. In addition, due to the nature of condensates they are highly miscible with resins and can maintain the fire-retarding and the radiation-resisting properties consistently for a long time (Japanese Patent Laid-Open Application No. Sho 56-122862).
The present invention aims to provide a process for producing brominated acenaphthylene condensates which are excellent in their radiation-resisting and fire-retarding properties.
2. Description of Prior Art
A known method to produce brominated acenaphthylene condensates comprises bromination and condensation of acenaphthene to prepare brominated acenaphthene condensates, followed by dehydrobromination.
Previously proposed methods of preparing brominated acenaphthene condensates are as follows: acenaphthene is brominated and condensed at the same time using iron (III) chloride as catalyst and 6 times as much moles of bromine as the acenaphthene at a reaction temperature between 25.degree. and 30.degree. C. (Y. Morita and M. Hagiwara, J. Appl. Polym. Sci., 27, 3329(1982); and brominated acenaphthene containing bromines at the aryl- and benzyl-positions of acenaphthene are condensed in the presence of a catalyst (Japanese Patent Laid-Open Application No. Sho 56-122862). The brominated acenaphthene condensates thus produced are treated with potassium hydroxide-methanol and others to obtain brominated acenaphthylene condensates.
In the former method, however, where the bromination reaction proceeds parallel to the condensation reaction, a large amount of polybrominated by-products of acenaphthene monomers is produced, leading to a low yield of the brominated acenaphthylene condensates.
In the latter method, proposed are the methods involving condensation of, for example, 1,2,3,5-tetrabromoacenaphthene using tin (IV) chloride or sulfuric acid as catalyst. However, the Japanese Patent Laid-Open Application does not refer to the yield and does not teach how to prepare the starting materials.
The present inventors have found on carrying out the above reaction that, due to low reactivity of the species, a significant amount of unreacted monomers remain in the reaction solution, leading to a low yield.
When the reaction was carried out in the presence of an active Lewis acid catalyst such as aluminum chloride, the product composition showed an extremely high degree of condensation, but an unignorable amount of bromine at the benzyl position was lost which was unfavorable to the double bond formation in the dehydrobromination reaction.
Further, the acenaphthene derivative as starting material containing bromines at the aryl- and benzyl-positions can be obtained only by troublesome and difficult processes with a low yield, if industrially readily available acenaphthene is used as raw material of the process.
Production of the brominated acenaphthylene condensates from acenaphthene as raw material, when conducted in a known process, has given only unsatisfactory results as an industrial process owing to the low yield.
The present inventors formerly found, for producing brominated acenaphthylene condensates, to carry out the bromination and condensation of acenaphthene at the same time at a temperature above 60.degree. C. and proposed the process. The preliminary object could be largely attained by the process, but by-production of polybrominated acenaphthene monomers could not be avoided. Therefore, the process did not meet the final object, though a better yield in the productin of the condensates was obtained than that in the previous known process.
The brominated acenaphthylene condensates of this invention are those compounds which contain at least one bromine atom per aromatic ring. Formally, the brominated acenaphthylene condensates are obtained by the condensation reaction of brominated acenaphthene in the course of Friedel-Crafts reaction to give a polymer having a degree of condensation of 2 or more, followed by the dehydrobromination reaction.
In forming the condensates, intermolecular combination is made between carbon atoms at the benzyl-position and those at the aryl-position of acenaphthylene. The benzyl-position in this invention refers to the side chain of the acenaphthene ring and the aryl-position refers to the naphthalene rings.
Examples of the combination are shown in the following formulae: ##STR5## Possible combinations include 1 (or 2), 3'-; 1 (or 2), 4'-; 1 (or 2), 7'-; 1 (or 2), 8'- and so on. Those having the degree of condensation of more than 2 are prepared by increasing the number of unit molecules according to any of these combination.
The condensates aimed at in this invention are a mixture of condensates having a degree of condensation not larger than 10 with good miscibility with resins.
Higher condensates having a degree of condensation greater than 10 show poor dispersion power into and poor miscibility with resin compositions, leading to discouraging effects on administration. On the other hand, monomers remaining uncondensed may likely to cause drawbacks in practice such as adherence to a roller when mixed with a resin and kneaded with the roller, or bleading on the resin surface in the form of pollen-like powder.
In conclusion, a preferred degree of condensation lies in the range from 2 to 9 and this achieved by controlling the reaction condition. However, in the conventional processes, the most predominant products consist mainly of monomers and lower condensates of dimers which are largely susceptible to bleading. Up to now, the degree of condensation has not been able to be controlled in the conventional processes of production.
Regarding dehydrobromination of the brominated acenaphthene condensates, it is known to dropwise add an ethanolic-solution of potassium hydroxide in an aromatic hydrocarbon solvent such as benzene (Japanese Laid-Open Patent Application No. Sho 56-122862) and it is proposed to dropwise add a methanolic solution of potassium hydroxide in a halogenated hydrocarbon solvent such as carbon tetrachloride as proposed by the present inventors in Japanese Patent Application No. Sho 57-169835 (U.S. patent application Ser. No. 537581).
In these methods, when the dehydrobromination is carried out with potassium hydroxide dissolved in a lower alcohol, a nucleophilic substitution reaction of the alkoxyl group occurs competitively and some etheric compounds are formed as by-products. If these by-products contaminate the Con-BACN, the thermal stability of the latter will be lowered so that purification is necessitated in such cases as in the method proposed by the present inventors (Japanese Patent Application No. Sho 57-193145; U.S. patent application Ser. No. 537581).
If potassium hydroxide is replaced by cheaper sodium hydroxide, a larger amount of alcohol is needed because of the smaller solubility of the latter hydroxide and hence a lower concentration of the base inevitably makes the reaction rate slower.
Further, if the dehydrobromination reaction is carried out in an aromatic hydrocarbon solvent, a troublesome operation should be included. Since the preceding reactions, that is bromination and condensation, must be conducted in a halogenated hydrocarbon solvent as an established art, an additional process is required to convert the solvent from a halogenated hydrocarbon to an aromatic hydrocarbon.
Therefore, a process using the same solvent through bromination, condensation and dehydrobromination is more advantageous and profitable.
However, it was found that, when the dehydrobromination is carried out in a halogenated hydrocarbon solvent, a small fraction of the solvent undergoes decomposition. Thus, carbon tetrachloride is decomposed as follows; EQU CCl.sub.4 +6KOH.fwdarw.K.sub.2 CO.sub.3 +3H.sub.2 O+4KCl
In addition, an alcoholic solution of potassium hydroxide which is added to a solution of brominated acenaphthene condensates should be prepared by dissolving solid potassium hydroxide in alcohol. This is a cumbersome operation and projects a problem on the worker's safety particularly because the process of this invention involves a batch-type reaction.
Furthermore, the reaction proper proceeds in two phases, that is, a solution of brominated acenaphthene condensates and an alcoholic solution, and therefore as the reaction progresses a large amount of potassium bromide salt is deposited, which adheres on the wall of reaction vessel or blades of stirrer and causes troublesome operations after the reaction.
Thus, as has been described above, the known processes of dehydrobromination are by no means satisfactory from the point of view of quality of products and of economical and operational estimation as an industrial technology.
Further, regarding the process for separating and recovering Con-BACN from the Con-BACN solution produced from acenaphthene as starting material the following methods may be considered;
(1) to distil the Con-BACN solution to remove the solvent; or
(2) to add the Con-BACN solution to a poor solvent to precipitate and separate Con-BACN.
However, the method (1) causes resin-like coagulation of Con-BACN so that powder Con-BACN cannot be obtained, and the handling operation is difficult.
Although the resin-like Con-BACN as it stands can be practically used, it contains a small amount of the solvent remaining therein, which is relatively difficult to remove. Therefore, the melting point f the resultant Con-BACN is 50.degree. to 80.degree. C. which is 50.degree. to 70.degree. C. lower than that of the powder Con-BACN, and when admixed with resin by rolls it easily sticks to the rolls and causes corrosion of working and forming machines due to thermal decomposition of the solvent.
In this connection, if the solvent contained in Con-BACN can be removed to obtain powder Con-BACN having a higher melting point, great advantages can be achieved with respect to the handling and roll mixing operation.
Meanwhile, regarding the method (2), it is known to add a solution of Con-BACN to acetone which is one of the poor solvent, and to reprecipitate powder Con-BACN (Y. Morita and M. Hagiwara, J. Appl. Polym. Sci., 27 3329(1982)). However, as Con-BACN will be dissolved in acetone to some degree the Con-BACN obtained by the reaction must preliminarily be condensed and then added to cold acetone (0.degree.--10.degree. C.) for reprecipitation. Therefore, the whole process is complicated and the yield of Con-BACN is low.
Extensive investigations have been conducted on producing brominated acenaphthylene condensates by the present inventors using acenaphthene as raw material, and it has been found with success that side-chain brominated acenaphthenes can be obtained with a high selectivity when acenaphthene is brominated with bromine under the ultraviolet irradition or in the presence of a radical initiator. The products thus obtained are a mixture of mono-, di- and tri-bromides depending on the amount of bromine added, and it has been found that, among the bromides, the monobromide in particular can be readily condensed under a mild condition with catalysts which are called strongly active or even with moderately or less active Lewis acid catalysts and the degree of condensation does not exceed 10, the strongly active Lewis acid catalysts including, for example, AlCl.sub.3, AlBr.sub.3 and GaCl.sub.3 and the moderately or less active ones including TiCl.sub.4, FeCl.sub.3, SbCl.sub.5, SnCl.sub.4 and ZnCl.sub.2. More particularly, side-chain monobromides could be formed with relatively high selectivity by controlling the amount of bromine to 0.2 to 2.0 times as much in moles as that of acenaphthene. The monobromides thus obtained are subjected to the condensation reaction using a Lewis acid catalyst and the product condensates are brominated using more than an equimolar amount of bromine to the acenaphthene. Thus, bromination reaction of acenaphthene occurs with a good balance between at the aryl- and the benzyl-positions, in parallel with the proceeding condensation reaction. As a result, the inventors found that intermediates of brominated acenaphthylene condensates could be obtained with a high yield of which condensates of the degree of condensation of 2 to 10 were the main constituents, and they could reach the development of this invention.
Further, the present inventors intensively investigated the dehydrobromination reaction and it has been found that when brominated acenaphthene condensates dissolved in a halogenated hydrocarbon solvent is dehydrobrominated with an alkali metal hydroxide, use of a mixture of water and alcohol in which ratio of water to alcohol is 0.1 to 0.5 by weight as the solvent of said alkali metal hydroxide could remarkably overcome the difficulty of previous arts. The present invention has thus come to completion.
In short, the increased concentration of the alkali metal hydroxide according to this invention has made it possible to conduct the dehydrobromination reaction without leading to decreased rate of the reaction due to water addition. In addition, the formerly mentioned side reaction could be remarkably suppressed by using said anhydrous alcohol. Obtained Con-BACN has good quality because the nucleophilic reaction of alkoxyl group disappears. In addition, this process is economically advantageous because decomposition of the halogenated hydrocarbon solvents is markedly suppressed.
In the method of this invention, the operation to dissolve solid caustic alkali is no more needed because the alkali metal hydroxide in an aqueous solution is only added to alcohol to prepare an alkali solution of a desired concentration. This implys remarkable improvement in workability.
Furthermore, when an aqueous alcohol solution is used, the alkali metal salt that is produced in the reaction remains dissolved in the solution and therefore it makes easy the treatment after completion of the reaction.
Thus, the present invention provides a process, as a part of a whole process, for economically producing Con-BACN from brominated acenaphthene condensates by a simple procedure.
Further, the present inventors investigated in details on the dehydrobromination reaction of brominated acenaphthene condensates without using a lower alcohol. It has been found that the dehydrobromination reaction proceeded very slowly without reaching completion if the condensates were dissolved in an organic solvent wich was immiscible with water and brought into contact with an aqueous solution of an inorganic metal baase to react in a two-phase system. They also found that, if the reaction was conducted in a severe condition to accelerate the reaction rate, alcohol derivatives of brominated acenaphthene were produced as by-product which led to lower to yield of Con-BACN. The contaminating alcoholic compounds may probably cause degraded qualities such as thermal stability, and therefore should be prevented.
In the more intensified investigation of the dehydrobromination reaction in the two-phase system, the inventors could reach the conclusion that the reaction could be completed in a shorter period of time when a quaternary ammonium salt was applied as a phase transfer catalyst, while crown ethers when used as the phase transfer catslysts could reveal no effect. Thus they could succeded in remarkable improvement of the known techniques and complete the present invention.
The dehydrobromination reaction in the two-phase system using crown ethers and quaternary ammonium salts as phase transfer catalyst are generally known. However, the known processes may cause various side reactions in the dehalogenation reactions of secondary alkylhalides such as appears in the present invention, and therefore they do not deserve accomplished methods.
For example, A. W. Herriott and others (Tetrahedron Letters, 44, 4521(1972)) found that a reaction of 2-bromooctane with an aqueous solution of sodium hydroxide in the presence of a quaternary ammonium salt in a two-phase system mainly produced octenes by the E2-type elimination reaction but a Sn 2-type substitution reaction occurred as a side reaction to produce 2-octanol in addition to said olefins. C. L. Liotta et al. (J. Am. Chem. Soc., 96, 2250(1974)) found that a non-aqueous reaction of 2-chloro-2-methylcyclohexanone with KF in acetonitrile in the presence of 18-crown-6 caused elimination (69%) and substitution (31%) of the F ion.
Thus, an elimination reaction and a nucleophilic reaction occur competitively in the reaction of a secondary or tertiary alkylhalide with an inorganic metal base in the presence of a phase transfer catalyst so that one cannot predict a single product.
However, in the process of this invention, only the dehydrobromination reaction of brominated acenaphthene condensates occurs selectively, and any by-product formation as a result of nucleophilic reaction is seen and decomposition of halogenated hydrocarbons does not occur, which could not have predicted from previously known arts and provides an industrially very useful process. In other words, the side reactions mentioned above could be completely suppressed by the process of the present invention. More particularly, the present invention does not use any alcohol solvent so that a nucleophilic reaction due to alkoxy group and a by-product of alcohol derivative are not seen at all. Therefore the Con-BACN obtained is of a high quality. In addition, no decomposition of halogenated hydrocarbon means an economical profit.
Again, the process of this invention permits the dehydrobromination reaction of brominated acenaphthene condensates to be completed in a very short period of time under mild conditions. In addition, since the process of this invention is carried out in two phases, organic and aqueous, inorganic metal salts that are formed as the reaction proceeds are dissolved in the aqueous phase and suppressed from depositing so that the treatment after the reaction becomes easier.
Therefore, the process of the present invention is provided as one of the integrated processes for the production of Con-BACN, comprising making brominated acenaphthene condensates dissolved in an organic solvent in contact with an aqueous solution of an inorganic metal base in the presence of a phase transfer catalyst.
Further, the present inventors have conducted extensive studies on various types and kinds of poor solvents for improving the yield of Con-BACN by simple operation in a reprecipitation process for recovering powder Con-BACN using poor solvents, and hae found that it is possible to recover powder Con-BACN by a simple operation yet with a high degree of yield when a monohydric alcohol of saturated aliphatic compounds having 3 to 5 carbon atoms is used.
Therefore, one aspect of the present invention is to provide a process for separating and recovering Con-BACN applicable to the production of Con-BACN solution obtained from acenaphthene through bromination, condensation and dehydrobromination of acenaphthene, which is characterized by adding the Con-BACN solution to a monohydric alcohol of saturated aliphatic compounds having 3 to 5 carbon atoms to precipitate powder Con-BACN.
The present inventors have made further investigations on poor solvents which permit precipitation of powder Con-BACN from the Con-BACN solution at a high degree of yield and also facilitate the separation between the solvents of the Con-BACN solution and the poor solvents, and have found that when the Con-BACN solution is added to a saturated aliphatic hydrocarbon having 5 to 9 carbon atoms powder Con-BACN can be recovered at a relatively high degree of yield and that the saturated aliphatic hydrocarbon can be separated easily by distillation after reprecipitation, because it has a boiling point different from that of the halogenated hydrocarbons or aromatic hydrocarbons used as the solvent of the Con-BACN solution and they don't form azeotropic mixture in distillation.
The present inventors have made still further investigations on the separation and recovery of Con-BACN on a commercial base, and found that powder Con-BACN of high quality can be obtained at a high degree of yield when the following process is repeated. Con-BACN solution using a good solvent is added to a poor solvent of saturated aliphatic hydrocarbons having 5 to 9 carbon atoms and having a boiling point higher than that of the good solvent to reprecipitate powder Con-BACN, then the slurry is removed of the good solvent by distillation, the resultant Con-BACN slurry is filtered to separate the powder Con-BACN and the filtrate is circulated to the poor solvent inthe reprecipitation step.